This invention relates generally to a gas turbine and, more particularly, to a gas turbine that incorporates essential features of a pressurized fluidized bed combustor cycle.
Gas turbine systems have been developed for generating electrical power which can use coal as a primary fuel source. In particular, systems have been developed in which the combustion of coal is carried out in a pressurized fluidized bed combustor (PFBC). Thus, referring to FIG. 1, there is schematically shown therein components of an exemplary advanced PFBC cycle. As will be appreciated, various components; sub-systems; and air, water/steam, and solids flowlines are omitted from the illustrated system for clarity and ease of explanation. In the illustrated system, ambient air 10 enters the compressor section 12 of the gas turbine 14 and is compressed. Compressor discharge air (80-100% of the total) is withdrawn as at 16 from the turbine 14. A major portion 18 of the compressed air extracted from the compressor 12 is directed to a PFBC 20 and a lesser portion 22 is used in, e.g., a fluid bed heat exchanger 24. The PFBC 20 is a combustion chamber in which a solid fuel is maintained in a fluidized bed to promote combustion. The solid fuel, may be a char 26 produced by a carbonizer 28, as discussed in further detail below. Thus, the compressed air extracted from the compressor and directed to the PFBC 20 fluidizes the bed and at the same time supplies the oxygen necessary for the solid fuel therein to be combusted. As a result of the combustion of the solid fuel, a hot compressed gas 30 is produced by the PFBC 20. The hot gas 30, vitiated by the combustion products, flows through a cyclone separator 32 to remove the particulate matter entrained in the gas, through a flue gas cooler 34, and a ceramic filter 36. Thereafter the hot gas 30, at about 1300.degree. F. to 1700.degree. F., is directed to the combustion section 40 of the gas turbine 14.
Another portion 42 of the air 16 extracted from the compressor discharge is boosted in pressure with a boost compressor 44 and used within the carbonizer 28. The carbonizer 28 is supplied with coal, which it converts to a carbonaceous char 26 and a hydrocarbon-based gas 46. The carbonaceous char 26, as mentioned above, is burned in the PFBC 20. The low BTU fuel gas (syngas) 46, which is generated from the coal or other carbonaceous fuel under reducing conditions, flows through a cyclone separator 48, fuel gas cooler 50, and ceramic filter 52 before the thus filtered fuel gas 54 is directed to the combustion section 40 of the gas turbine 14. The syngas 54 (at about 1200.degree. F. to 1600.degree. F.) is burned in the combustion section 40 of the gas turbine 14 using the hot vitiated gas 38 from the PFBC 20, allowing for maximum utilization of the coal.
The high temperature gas 56 from the combustion section 40 flows through the turbine section 58 where the hot gas expands thereby producing power in the rotating shaft 60 of the gas turbine 14. The temperature of the gas 62 after expansion in the turbine section 58, although reduced, is still relatively high. Thus, to increase efficiency of the system, the expanded and partially cooled gas 62 exhausting from the turbine section 58 is directed to a heat recovery steam generator (HRSG) 64 where the gas is further cooled by the transfer of heat to feed water. The steam generated by the HRSG is expanded in a steam turbine (not shown) in a known manner thereby producing additional electrical power. The HRSG and steam turbine are operatively coupled in a known manner (not shown) to, e.g., the carbonizer, the fluid bed heat exchanger, and/or the fuel gas coolers. The cooled vitiated gas 66 exhausting from the HRSG 64 is then discharged through a stack 68, to atmosphere.
While the PFBC cycle described above provides high cycle efficiency, as noted it requires substantially full extraction of compressor discharge air to feed the carbonizer and the PFBC. This PFBC cycle also requires use of the high temperature vitiated air for combustion. Neither full extraction of compressor discharge air nor the use of high temperature vitiated air is possible with conventional combustion turbines.